Sin is a very serious matter. Our sins are why Jesus died
on a cross. Sin is what separates us from God:

Isaiah 59:1-2

Surely
the arm of the LORD is not too short to save, nor his ear too dull to hear. But
your iniquities have separated you from your God; your sins have hidden his
face from you, so that he will not hear.

Who is a sinner? Everyone is a sinner! That is why every
single human being needs Christ.

Isaiah 64:5-6

All of us have become like one who is unclean, and all our
righteous acts are like filthy rags; we all shrivel up like a leaf, and like
the wind our sins sweep us away. No one calls on your name or strives to lay
hold of you; for you have hidden your face from us and made us waste away
because of our sins.

Romans 3:10-12,23

As
it is written: “There is no one righteous, not even one; there is no one who
understands, no one who seeks God. All have turned away, they have together
become worthless; there is no one who does good, not even one…

for
all have sinned and fall short of the glory of God

What is sin? Sin means to “miss the mark.” It means to
“fall short.” Simply put, sin is wrongdoing.

Here are some passages where the Bible defines sin:

Galatians 5:19-21

The
acts of the sinful nature are obvious: adultery, fornication, impurity,
licentiousness, idolatry, sorcery and witchcraft, hatred, discord, jealousy,
fits of rage, selfishness, dissension, party spirit, envy, murder, drunkenness,
carousing, and the like. I warn you, as I warned you before, that those who
live like this shall not inherit the kingdom
of God.

Colossians 3:5-10

Put to death, therefore, whatever belongs to
your earthly nature: sexual immorality, impurity, lust, evil desires and greed,
which is idolatry. Because of these, the wrath of God is coming. You used to
walk in these ways, in the life you once lived. But now you must rid yourselves
of all such things as these: anger, rage, malice, slander, and filthy language
from your lips. Do not lie to each other, since you have taken off your old
self with its practices and have put on the new self, which is being renewed in
knowledge in the image of its Creator.

Mark 7:20-22

And
he said, “What comes out of a man is what defiles a man. For from within, out
of the heart of man, come evil thoughts, fornication, theft, murder, adultery,
coveting, wickedness, deceit, licentiousness, envy, slander, pride, and
foolishness.

Revelation 21:7-8

He
who conquers shall have this heritage, and I will be his God and he shall be my
son. But as for the cowardly, the faithless, the polluted, as for murderers,
fornicators, sorcerers, idolaters, and all liars, their lot shall be in the
lake that burns with fire and sulphur, which is the second death.”

James
4:17

Anyone,
then, who knows the good he ought to do and doesn’t do it, sins.

What is the penalty for sin?

Romans 6:23

Forthe wages of sin is death,but the gift
of God is eternal life in Christ Jesus our Lord.

It only took one sin for Adam and Eve to die spiritually.
That is how serious and deadly sin is to us.Once we have sinned, we
die and become separated from God and are in need of the Redeemer and the
forgiveness that is made possible through the work Jesus did on the cross.